Summary

cDNA clones complementary to poly(A)-containing RNA from ovarian follicle cells of Drosophila have been prepared. On the basis of restriction mapping and cross hybridization tests, 22 such clones were found to comprise four classes (group l-group IV). Filter-bound DNA from clones in each group hybrid-ized, under stringent conditions, with a single size class of ovarian poly(A)-containing RNA. The mobil-ities of these RNAs on gels corresponded to those of putative chorion messenger RNAs (Spradling and Mahowald, 1979). Translation of the RNAs in vitro yielded proteins with apparent molecular weights lDDD-3DW daltons greater than those of mature chorion proteins isolated from purified eggshells. When a membrane fraction from dog pancreas was included in the in vitro translation reaction, the mobilities of the products were indistinguishable from those of major chorion proteins in three cases: c38 (group I), c36 (group II) and cl8 (group Ill). The 16K product of hybrid-selected RNA from group IV clones could not be associated unambiguously with a specific chorion protein. Hybridization of cloned cDNAs to restriction digests of DNA prepared from embryonic nuclei was consistent with the presence of one (~38 and ~36) or several (~18) copies of these genes per haploid Qenome. Hybridization in situ of RNA transcripts from the clones to polytene chromosomes demonstrated that the genes for these four proteins are clustered at two sites. In agreement with previous results (Spradling, Waring and Mahowald, 1979), both c36 and c38 are coded at 7Ell-7Fl-2 on the X chromosome. Group Ill and group IV clones were both localized at a site on the third chromosome (66D15). l To whom correspondence should be addressed at: Department o